1. Field of the Invention
The present invention relates to a guide for a chain drive provided on an engine body.
2. Description of the Related Art
Conventionally, chain drives installed on an engine body having a cylinder block and a cylinder head are classified into two types according to the way of mounting a guide to the engine body.
A first type of conventional chain drive is shown in FIG. 8A and includes a guide 11 mounted to an engine body so that it extends over a cylinder block 1 and a cylinder head 6 of the engine body. In the chain drive, a chain 9 is trained around a sprocket (crank sprocket) 7 rotatably mounted on the cylinder block 1 and two sprockets (cam sprockets) 8, 8 rotatably mounted on the cylinder head 6, and a tensionder device 10 is disposed on the exterior side of a slack run of the chain 9 for applying an appropriate tension to the chain 9. The guide 11 for the chain drive is disposed on the exterior side of a tension run of the chain 9 for preventing oscillation of the chain 9 while running.
The tensioner device 10 is comprised of a tensioner lever 10B pivotally connected at one end to a mounting surface of the cylinder block 1, and a tensioner 10A for urging a free end portion of the tensioner lever 10B against the chain 9. By a biasing force of the tensioner 10A, a shoe surface of the tensioner lever 10B is forced against the slack run of the chain 9 so that an appropriate tension is applied to the chain 9.
The guide 11 has two mounting portions provided near opposite longitudinal ends of the guide 11 and each formed with one circular mounting hole (not show) . A screw 14 is inserted through the mounting hole of one mounting portion (upper mounting portion) and threaded into a threaded hole (not shown) formed in the cylinder head 6. Similarly, a screw 14 is inserted through the mounting hole of the other mounting portion (lower mounting portion) and threaded into a threaded hole (not shown) formed in the cylinder block 1. The guide 11 is thus mounted to the engine body by means of the screws 14.
A second type of conventional chain drive is shown in FIG. 9A and includes a guide 13 mounted to a cylinder block 4 of an engine body. In the chain drive used on the engine body comprised of the cylinder block 4 and a cylinder head 6, a chain 9 is trained around a cylinder block side sprocket (crank sprocket) 7 and two cylinder head side sprockets (cam sprockets) 8, 8, and a tensionder device 10 is disposed on the exterior side of a slack run of the chain 9 for applying an appropriate tension to the chain 9. The guide 13 for the chain drive is disposed on the exterior side of a tension run of the chain 9 for preventing oscillation of the chain 9 while running.
The tensioner device 10 is comprised of a tensioner lever 10B pivotally connected at one end to a mounting surface of the cylinder block 4, and a tensioner 10A for urging a free end portion of the tensioner lever 10B against the chain 9. By a biasing force of the tensioner 10A, a shoe surface of the tensioner lever 10B is forced against the slack run of the chain 9 so that an appropriate tension is applied to the chain 9.
The guide 13 has two mounting portions provided near opposite longitudinal ends of the guide 13 and each formed with one circular mounting hole (not shown). Two screw 14 are inserted through the respective mounting holes of the upper and lower mounting portions and threaded into threaded holes (not shown) formed in the cylinder block 4, whereby the guide 13 is mounted to the cylinder block 4 by means of the screws 14.
In an engine, there is a case where the cubic capacity or displacement of the engine is changed by replacing the cylinder block with another cylinder block having a different height while the cylinder head remains unchanged.
FIG. 8B shows a right half of the chain drive which is used on an engine body whose cubic capacity has been changed by using a cylinder block 2 having a different height than the cylinder block 1 shown in FIG. 8A.
As shown in FIG. 8B, in the case where the cubic capacity of the engine is changed by using a cylinder block 2 of a different height (larger height) in combination with the existing cylinder head 6, in order to use the same guide 11 in common, the distance or pitch P1 between the threaded hole in the cylinder head 6 and a threaded hole in the cylinder block 2 must be made equal to the distance or pitch P1 between the threaded hole in the cylinder head 6 and the threaded hole in the cylinder block 1. To this end, the position of the threaded hole formed in the cylinder block 2 is displaced upward from that of the threaded hole in the cylinder block 1 by a distance h which is equal to a difference in height between the cylinder blocks 2 and 1. There arises a problem that the same working or processing cannot be used for forming threaded holes in more than two cylinder blocks of different sizes (heights).
As shown in FIG. 8C, in the case where the cubic capacity of the engine is changed by using a cylinder block 3 of a different height in combination with the existing cylinder head 6, if the use of the same processing on the cylinder block takes preference over the use of the same guide, a threaded hole in the cylinder block 3 is formed at the same position as the threaded hole in the cylinder block 1 shown in FIG. 8A. Due to a difference in pitch between the threaded hole of the cylinder head and the threaded hole of the cylinder block, the same guide 11 cannot be used. To deal with this problem, a similar guide 12 must be provided, having two circular mounting holes spaced at the same distance or pitch as the pitch P2 between the threaded holes in the cylinder block 3 and cylinder head 6. As a consequence, similar guides of different sizes (lengths) must be provided, tending to cause confusion between them.
FIG. 9B shows a right half of the chain drive which is installed on an engine body whose cubic capacity has been changed by using a cylinder block 5 having a different height than the cylinder block 4 shown in FIG. 9A.
The guide 13 shown in FIG. 9A has two circular mounting holes (not shown) formed in two mounting portions provided near opposite longitudinal ends of the guide 13. Two screw 14 are inserted through the respective mounting holes of the upper and lower mounting portions of the guide 13 and threaded into two threaded holes (not shown) both formed in the cylinder block 4, whereby the guide 13 is attached by the screws 14 to the cylinder block 4. Accordingly, in the case where the cubic capacity of the engine is changed by replacing the cylinder block 4 with a cylinder block 5 of a different height while the cylinder head 6 remains unchanged, as shown in FIG. 9B, the same processing can be used in common such that two threaded holes are formed in the cylinder block 5 at the same position as those formed in the cylinder block shown in FIG. 9A. Thus, the same guide 13 can be used.
However, the chain drive shown in FIG. 9A and the chain drive shown in FIG. 9B differ from each other in the positional relationship between the guide 13 and an adjacent one of the cylinder head side sprockets (cam sprockets) 8. More specifically, the distance H2 (FIG. 9B) between the axis of the cam sprocket 8 and an adjacent end (upper end) of the guide 13 is larger than the distance H1 (FIG. 9A) between the axis of the cam sprocket 8 and the adjacent end of the guide 13. This means that the chain drive shown in FIG. 9A and the chain drive shown in FIG. 9B each have a different chain line or path extending between the cam sprocket 8 and the guide 13. Thus, the guides 13 shown in FIGS. 9A and 9B achieve different oscillation preventing effects with respect to the chain 9, tending to vary the acoustic and vibration characteristics of the chain drives.
With the foregoing drawbacks of the prior art in view, it is an object of the present invention to provide a guide for a chain drive, which is capable of being mounted to mounting to more than two engine bodies each having threaded holes of a different pitch.
To achieve the foregoing object, there is provided, according to one aspect of the present invention the present invention, a guide for a chain drive installed on an engine body having threaded holes formed therein with a pitch, wherein the guide has at least two mounting portions adapted to be attached to the engine body by means of screws threaded into the threaded holes in the engine body. At least one of the mounting portions has at least two circular mounting holes spaced in a longitudinal direction of the guide so that the guide can be also mounted to at least one similar engine body having threaded holes formed therein with a different pitch.
By properly selecting one mounting hole of the at least two mounting holes, the guide can be mounted to two or more engine bodies each having a different threaded hole pitch. The guide can be commonly used for more than two chain drives of different sizes. This makes it possible to reduce the costs required for the manufacture and inventory of parts of the chain drive and avoid confusion with a similar guide.
In the case where the guide attached to the engine body extends over a cylinder head and a cylinder block, the guide is readily adaptable to a modification in which the threaded hole pitch is caused to change due to the use of a cylinder block having a different height. This makes it unnecessary to change the position of the threaded holes formed in the engine body, so that the same working or processing can be used for forming threaded holes in cylinder blocks of different sizes (heights).
The circular mounting holes formed in the at least one mounting portion may be replaced with a single oblong hole elongated in the longitudinal direction of the guide. In this instance, the screw is set to take an appropriate position selectable within the longitudinal extremities of the oblong hole.
According to a second aspect of the present invention, there is provided a guide for a chain drive installed on an engine body including a cylinder block and a cylinder head wherein the chain drive includes a crank sprocket mounted on the cylinder block, a cam sprocket mounted on the cylinder head, and a chain trained around the sprockets, and the engine body has two threaded holes formed in the cylinder block and cylinder head, respectively, with a pitch. The guide has a first mounting portion adapted to be attached to the cylinder head by means of a first screw threaded into the threaded hole in the cylinder head and a second mounting portion adapted to be attached to the cylinder block by means of a second screw threaded into the threaded hole in the cylinder block. The first mounting portion has a single circular mounting hole for the passage therethrough of the first screw, and the second mounting portion has at least two circular mounting holes spaced in a longitudinal direction of the guide and each provided for the passage therethrough of the second screw, so that the guide can also be mounted, without changing a chain line extending between the cam sprocket and the guide, to at least one similar engine body having threaded holes formed therein with a different pitch due to the use of a cylinder block of a different height. The circular mounting holes formed in the second mounting portion may be changed to a single oblong hole elongated in the longitudinal direction of the guide.
The guide having at least two circular mounting holes or a single oblong hole in the second mounting portion is able to accommodate variations in height of the cylinder block without changing a chain line or path extending between the cam sprocket and the guide. Thus, the same chain oscillation preventing effect can be attained at all times regardless of a modification made to change the height of the cylinder body. The chain drive has the same acoustic and vibration characteristics regardless of the change in height of the cylinder block. It is important to note that since the acoustic and vibration characteristics of a chain drive are greatly influenced by a chain line located at an entrance side of the guide when viewed from the direction of travel of the chain, the aforesaid chain line (extending between the cam sprocket and the guide) should preferably be kept always constant.
According to a third aspect of the present invention, there is provided a guide for a chain drive installed on an engine body including a cylinder block and a cylinder head, wherein the chain drive includes a crank sprocket mounted on the cylinder block, a cam sprocket mounted on the cylinder head, and a chain trained around the sprockets, and the engine body has two threaded holes formed in the cylinder block and cylinder head, respectively, with a pitch. The guide has a first mounting portion adapted to be attached to the cylinder head by means of a first screw threaded into the threaded hole in the cylinder head and a second mounting portion adapted to be attached to the cylinder block by means of a second screw threaded into the threaded hole in the cylinder block. The first mounting portion has at least two circular mounting holes spaced in a longitudinal direction of the guide and each provided for the passage therethrough of the first screw, and the second mounting portion has a single circular mounting hole for the passage therethrough of the second screw, so that the guide can also be mounted, without changing a chain line extending between the crank sprocket and the guide, to at least one similar engine body having threaded holes formed therein at a different pitch due to the use of a cylinder block of a different height. The circular mounting holes formed in the first mounting portion may be replaced with a single oblong hole elongated in a longitudinal direction of the guide for the passage therethrough of the first screw.
The guide having at least two circular mounting holes or a single oblong hole in the first mounting portion is able to accommodate variations in height of the cylinder block without changing a chain line or path extending between the crank sprocket and the guide. Since the same guide can be used in common regardless of a change in height of the cylinder block, this arrangement is particularly advantageous when the length of a guide should be minimized due to a small space available around the crank sprocket for installation of the guide.